The present invention relates to a method of controlling an automatic disc clutch, the disc clutch being arranged in a motor vehicle in order to transmit motive force from an internal combustion engine to a gearbox.
The invention also relates to a control unit for controlling an automatic disc clutch.
The invention also relates to a computer program for carrying out said method.
Automatic Mechanical Transmissions (AMT:s) have become ever more common in heavier vehicles with the increasing development of microprocessor systems, making it possible, with a control computer and a number of control devices, such as servomotors, for example, to precisely regulate the engine speed, engagement and disengagement of an automatic disc clutch between engine and gearbox, and gearbox clutch members in relation to one another, so that smooth gear changes are always achieved at the correct engine speed. The advantage with this type of automatic gearbox compared to a conventional automatic gearbox made up of planetary gear trains and having a hydrodynamic torque converter on the inlet side lies partly in the fact that it is simpler and more robust and can be manufactured at substantially lower cost than the conventional automatic gearbox, especially where used in heavy vehicles, and partly in that it affords greater efficiency, which means scope for reduced fuel consumption.
A gearbox of the AMT-type usually comprises an input shaft, an intermediate shaft, which has at least one toothed gear meshing with a toothed gear on the input shaft, and main shaft with toothed gears, which mesh with toothed gears on the intermediate shaft. The main shaft is then further connected to an output shaft coupled to the driving wheels via a prop shaft, for example. Each pair of toothed gears has a different gear ratio from another pair of gears in the gearbox. Different transmission ratios are obtained in that different pairs of gears transmit the torque from the engine to the driving wheels.
The development of computer technology has also had an impact on electronic control and feedback systems for a vehicle engine, and these systems have become more precise, faster and more adaptable to prevailing engine and environmental conditions. The entire combustion process can be precisely controlled according to any operating situation. The vehicle's throttle lever (an accelerator pedal, for example), which primarily controls the fuel supply to the engine, controls the vehicle' s engine via electrical wiring and electronic signals. The throttle lever is therefore equipped with sensors for detecting the throttle lever position, that is to say what throttle opening is required.
In the process of starting or maneuvering the vehicle an automatic disc clutch as described above is included in the AMT and is usually controlled by means of information on the position of the throttle lever, the rotational speed of the engine, the engine output torque, the position of the disc clutch and from a reference position of the disc clutch, which is selected on the basis of when the disc clutch just begins to transmit torque (traction position), this position being relatively easy to define. A torque typically transmitted in the reference position may be in the order of 30 Nm. The engine output torque is mostly calculated from the quantity of fuel injected into the engine. In the starting sequence and maneuvering the vehicle is typically started from stationary or a virtually stationary state, and the engine commences the sequence at idling speed. The position of the disc clutch and hence the degree of engagement, which determines the torque transmitted from the engine to the gearbox, primarily depends on where the driver positions the throttle lever. The reference position of the disc clutch is used to give the driver of the vehicle more accurate control of the vehicle take off in that the disc clutch assumes the reference position immediately a starting gear is selected and engaged. The vehicle is prepared for immediate take off. Thus in many situations the driver experiences only a small flat spot, if any, when the accelerator pedal is depressed. The driver therefore obtains a theoretically direct response and the vehicle in principle starts to move as soon as the accelerator pedal starts to be depressed.
FIG. 1a shows the fundamental correlation between the position of the accelerator pedal and the torque transmitted to the input shaft of the gearbox according to the prior art. When the accelerator pedal is fully released and a starting gear is selected the disc clutch assumes the reference position and a certain torque is therefore transmitted to the input shaft of the gearbox. The more the driver depresses the accelerator pedal the more torque is transmitted to the gearbox and an acceleration of the vehicle is obtained. FIG. 1b correspondingly shows basically how, according to the prior art, the position of the disc clutch depends on the position of the accelerator pedal. With the accelerator pedal released the reference position (POSRF) is assumed, and from the reference position the disengagement diminishes the more the accelerator pedal is depressed, which gives the increasing torque transmission according to FIG. 1a. The maximum position in FIG. 1b denotes the clutch in the fully engaged position.
WO2004/005744 shows an arrangement where a clutch control system may also select a more disengaged position at zero throttle opening, if the control system does not receive signals indicating that the driver intends to start (vehicle take off) the vehicle, for example if the control system detects that the driver is keeping the vehicle brake pedal depressed.
According to prior art when a starting gear has been engaged and the clutch is positioned in said reference position, the vehicle is ready to response immediately when the driver of the vehicle depresses the accelerator pedal. If the driver does not depress the accelerator pedal and does not touch the brake pedal the clutch just continues to be positioned in said reference position, and, thus, a small torque is being transmitted to the gearbox even if the vehicle is standing still. This means that fuel is consumed for purely warming up and wearing down the clutch.
There is therefore a need, in a vehicle equipped with an automatic disc clutch, to decrease friction losses and clutch wear.
The method according to the invention describes a method for controlling the position of an automatic disc clutch, in which method the primary function of the disc clutch is to transmit motive force from an internal combustion engine arranged in a vehicle to an input shaft of a stagegeared gearbox arranged in the vehicle. The method is employed when the gearbox has a starting gear engaged and the clutch is positioned in a first position (PosRF), which prepares the vehicle for take off, and where in said first position the clutch transmits a smaller torque. The method is characterized in that if a driver of the vehicle does not demand vehicle take off torque by activating a throttle control within a predetermined time, said clutch will be positioned in a second more disengaged position (POS2) compared to said first position.
The advantage of the method according to the invention is that fuel will be saved and wear of the clutch will be decreased. The same advantages are achieved with an aspect of the invention relating to a device.
According to an advantageous second embodiment of the method according to the invention said clutch is positioned in said second position when sensing depression of the brake pedal if a brake pedal in the vehicle is depressed before said predetermined time has passed. The advantage of this is that even more fuel can be saved and wear of the clutch can be decreased. The driver indicates that there will not be any vehicle take off when the driver depresses the brake pedal, and thus, the vehicle does not need to be prepared for immediate vehicle take off.